This invention relates to a device for detecting deterioration of a sensor for detecting the temperature of a three-way catalyst installed in the exhaust pipe of an internal combustion engine.
A device for protecting a three-way catalyst installed in the exhaust pipe of an internal combustion engine by increasing the amount of fuel supplied to the engine when the temperature of the catalyst detected by a sensor fitted to the catalyst is above a predetermined value, is disclosed for example in Japanese Provisional Patent Publication (Kokai) No. 62-223427.
However, in this device, the sensor which detects the catalyst temperature also deteriorates with time so that it no longer performs accurate detection, and the catalyst is no longer protected. As a result, if the sensor indicates a lower value than the actual catalyst temperature, the amount of fuel supplied to the engine is not increased although the actual catalyst temperature is above the predetermined value. This impairs exhaust emission characteristics.
On the other hand, if the sensor indicates a higher value than the actual catalyst temperature, the amount of fuel supplied to the engine is increased unnecessarily and exhaust emission characteristics are again impaired.